The renegade monk Jean Buridan rebel against Aristotle. Followed up with Philoponus and further the concept of impetus. Breakaway from the shackles of Aristotle. But nature of impetus still unknown.

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JEAN BURIDAN
CM [004] The Renegade Monk

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Jean Buridan
Jean Buridan (1295-1358) was a
French priest credited to be the
person who sowed the seeds
for the Copernican revolution
in Europe.
Before Buridan, natural
philosophy was only a
handmaiden of theology or a
mere disciple after the
doctrines of Aristotle. After the
time of Buridan, it began to
have its own legitimacy and
developed in a new direction.

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Motion of Projectiles
Like Philoponus in the 6th century, Buridan was particularly in discordance with
Aristotle’s concept on motion of projectiles.
The trajectory of a projectile by Aristotle

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Buridan on Projectiles
Buridan said: “. . . after leaving the arm of the thrower, the projectile would be
moving by an ‘impetus’ given to it by the thrower and would continue to move as
long as the impetus remained stronger than the resistance, and would be of
infinite duration were it not diminished and corrupted by a contrary force
resisting it or by something inclining it to a contrary motion.”
IMPETUS

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Buridan’s Impetus
According to Buridan in his “Quaestiones on
Aristotle's Physics”:
“When a mover sets a body in motion he
implants into it a certain impetus:
[𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀 = 𝐼𝐼 𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼]
. . . a certain force enabling a body to move
in the direction in which the mover starts it,
be it upwards, downwards, sidewards, or in
a circle.
[𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷 𝑜𝑜𝑜𝑜 𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚 =
𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷 𝑜𝑜𝑜𝑜 𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖]

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Buridan’s Equation
The implanted impetus increases in the
same ratio as the velocity.
[𝐼𝐼 𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼 ∝ 𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉]
in fact, Buridan gave it a mathematical
formulation:
𝐼𝐼 𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼 = 𝑊𝑊𝑊𝑊𝑊𝑊 𝑊𝑊 𝑊𝑊𝑊 × 𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉
The weight is a constant that does not
change. So the impetus is purely a
function of velocity.
Faster object has greater impetus

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INERTIA
Impetus became Momentum
It can be said that what Buridan did was very close to defining momentum in the
Newtonian sense 𝒑𝒑 = 𝑚𝑚𝒗𝒗.
This impetus theory was revived in the thirteenth century by Peter John Olivi (c.
1248-1298) and has been incorporated into modern physics as momentum.
Buridan’s IMPETUS

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Nature of Impetus
Apparently Buridan’s way of
thinking was on the right track.
But again like Philoponus, he
did not investigate further why
it should be as he thought. It
seemed to him that it was an
elementary fact and resumed
no further explanation. What is
impetus? What is in impetus
that is passed on from one
body to another to make a
body move?
IMPETUS
?

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FRICTION
To be continued on: CM [005] The Discovery of
ABCC